1. Field of the Invention
The present invention relates to a high-frequency switch, and more particularly to a high-frequency switch for being incorporated in a mobile communications device and the like.
2. Description of the Related Art
A high-frequency switch is generally used for switching between a transmission circuit and a reception circuit in a digital mobile telephone and the like. FIG. 6 is an electrical circuit diagram showing a prior art high-frequency switch 1. The anode of a diode D1 is connected to a transmission terminal Tx. The anode of the diode D1 is grounded via a series circuit comprising a transmission line 2 and a DC-blocking capacitor C1. A voltage-control terminal Vc1 is connected via a resistor Ra at an intermediate connection point between the transmission line 2 and the capacitor C1. The cathode of the diode D1 connects to an antenna terminal ANT.
A reception terminal Rx is connected to the antenna terminal ANT via a transmission line 3. Moreover, the anode of a diode D2 is connected to the reception terminal Rx. The cathode of the diode D2 is grounded.
Here, the DC-blocking capacitor C1, connected between the transmission line 2 and the ground, has a large capacitance (approximately 47 pF near 1 GHz, and approximately 22 pF near 2 GHz). Since the size of the capacitor C1 connected between the transmission line 2 and ground is large, miniaturization of the high-frequency switch 1 is hindered.
Furthermore, in the high-frequency switch 1, when the transmission terminal Tx and the antenna terminal ANT are connected, isolation must be maintained between the antenna terminal ANT and the reception terminal Rx. When this isolation is poor, insertion loss between the transmission terminal Tx and the antenna terminal ANT increases.
The present invention provides a high-frequency switch which overcomes the above described problems, being small-scale and having superior performance.
One preferred embodiment of the present invention provides a high-frequency switch comprising:
a transmission terminal, an antenna terminal, a reception terminal, and a voltage-control terminal;
a first diode, the cathode thereof being electrically connected to said transmission terminal, and the anode being electrically connected to said antenna terminal;
a first transmission line, electrically connected between said antenna terminal and said reception terminal;
a second diode, the cathode thereof being electrically connected to said reception terminal, and the anode being electrically connected to said voltage-control terminal;
a second transmission line, one end thereof being electrically connected to said transmission terminal, and the other end being connected to ground; and
a capacitor, electrically connected between said voltage-control terminal and ground.
With the above constitution, there is no need for the conventional large-capacitance capacitor which was connected on the transmission terminal side, and it is sufficient to connect only a small-capacitance capacitor on the reception terminal side. Therefore, the high-frequency switch can be miniaturized.
In the above described high-frequency switch, said transmission terminal, said reception terminal, said antenna terminal, and said voltage-controlled terminal may be provided on the surface of a multilayered body; said multilayered body being formed by laminating a plurality of dielectric layers, said first and second transmission lines, a capacitor electrode of said capacitor and a ground electrode; and said first and second diodes may be mounted on said multilayered body. Alternatively, the capacitor may be mounted on the surface of the multilayered body, instead of being contained in the multilayered body.
According to the constitution described above, a high-frequency switch is obtained having a multilayered structure wherein the circuit is contained within a single component.